RSVP can be used by hosts and routers to reqwest or dewiver specific wevews of QoS for appwication data streams or fwows. RSVP defines how appwications pwace reservations and how dey can rewinqwish de reserved resources once no wonger reqwired. RSVP operation wiww generawwy resuwt in resources being reserved in each node awong a paf. RSVP is not a routing protocow and was designed to interoperate wif current and future routing protocows.

RFC 2205: The version 1 functionaw specification was described in RFC 2205 (Sept. 1997) by IETF. Version 1 describes de interface to admission (traffic) controw dat is based "onwy" on resource avaiwabiwity. Later RFC2750 extended de admission controw support.

RFC 4495, "A Resource Reservation Protocow (RSVP) Extension for de Reduction of Bandwidf of a Reservation Fwow" (May 2006), extends RSVP to enabwe de bandwidf of an existing reservation to be reduced instead of tearing down de reservation, uh-hah-hah-hah.

RSVP reserves resources for a fwow. A fwow is identified by de destination address, de protocow identifier, and, optionawwy, de destination port. In muwtiprotocow wabew switching (MPLS) a fwow is defined as a wabew switched paf (LSP). For each fwow RSVP awso identifies de particuwar qwawity of service reqwired by de fwow awdough it does not understand de specific information of de fwow QoS. This QoS specific information is cawwed a fwowspec and RSVP passes de fwowspec from de appwication to de hosts and routers awong de paf. Those systems den anawyse de fwowspec to accept and reserve de resources. A fwowspec consists of:

The fiwterspec defines de set of packets dat shaww be affected by a fwowspec (i.e. de data packets to receive de QoS defined by de fwowspec). A fiwterspec typicawwy sewects a subset of aww de packets processed by a node. The sewection can depend on any attribute of a packet (e.g. de sender IP address and port).

An RSVP reservation reqwest consists of a fwowspec and a fiwterspec and de pair is cawwed a fwowdescriptor. The effects at de node of each spec are dat whiwe de fwowspec sets de parameters of de packet scheduwer at a node, de fiwterspec sets de parameters at de packet cwassifier.

The resv message is sent from de receiver to de sender host awong de reverse data paf. At each node de IP destination address of de resv message wiww change to de address of de next node on de reverse paf and de IP source address to de address of de previous node address on de reverse paf.

An RSVP host dat needs to send a data fwow wif specific QoS wiww transmit an RSVP paf message every 30 seconds dat wiww travew awong de unicast or muwticast routes pre-estabwished by de working routing protocow. If de paf message arrives at a router dat does not understand RSVP, dat router forwards de message widout interpreting de contents of de message and wiww not reserve resources for de fwow.

Those who want to wisten to dem send a corresponding resv (short for "Reserve") message which den traces de paf backwards to de sender. The resv message contains de fwow specs. When a router receives de RSVP resv message it wiww:

Make a reservation based on de reqwest parameters. For dis de admission controw and powicy controw process de reqwest parameters and can eider instruct de packet cwassifier to correctwy handwe de sewected subset of data packets or negotiate wif de upper wayer how de packet handwing shouwd be performed. If dey cannot support de reservation being reqwested, dey send a reject message to wet de wistener know about it.

Forward de reqwest upstream (in de direction of de sender). At each node de resv message fwowspec can be modified by a forwarding node (e.g. in de case of a muwticast fwow reservation de reservations reqwests can be merged).

The routers den store de nature of de fwow, and awso powice it. This is aww done in soft state, so if noding is heard for a certain wengf of time, den de reader wiww time out and de reservation wiww be cancewwed. This sowves de probwem if eider de sender or de receiver crash or are shut down incorrectwy widout first cancewwing de reservation, uh-hah-hah-hah. The individuaw routers may, at deir option, powice de traffic to check dat it conforms to de fwow specs.

The resv message awso has FiwterSpec object; it defines de packets dat wiww receive de reqwested QoS defined in de fwowspec. A simpwe fiwter spec couwd be just de sender’s IP address and optionawwy its UDP or TCP port.

Integrity - RSVP messages are appended wif a message digest created by combining de message contents and a shared key using a message digest awgoridm (commonwy MD5). The key can be distributed and confirmed using 2 message types: integrity chawwenge reqwest and integrity chawwenge response.

Error reporting - when a node detects an error, an error message is generated wif an error code and is propagated upstream on de reverse paf to de sender.

Information on RSVP fwow - two types of diagnostic messages awwow a network operator to reqwest de RSVP state information on a specific fwow.